There might be a better way, but what you'll want to find or create a hex grid pattern. The create a pattern in photoshop. Create a new top layer, fill with white and go to layer styles. Fill the layer with your pattern, size to your liking and then multiply the top layer with the layers below. If you can want a different look for your overlay, you can always flatten that layer with another newly created layer, then select the white and delete it, leaving you with a black line overlay that you can now try using other blending options.